1. Field of the Invention
The invention generally relates to the field of semiconductor power devices. More particularly, the present invention relates to a lateral stack-type super junction power semiconductor device.
2. Description of the Prior Art
Power devices are mainly used in power management; for instance, in switching power supplies, in management integrated circuits in the core or peripheral regions of computers, in backlight power supplies, and in electric motor controls. This type of power devices, as described above, includes an insulated gate bipolar transistor (IGBT), a metal-oxide-semiconductor field effect transistor (MOSFET), or a bipolar junction transistor (EU), among which the MOSFET is the most widely utilized because of its energy saving properties and its ability to provide faster switch speed.
In one kind of power device, a P-type epitaxial layer and an N-type epitaxial layer are alternatively disposed to form several vertical PN junctions inside a structure, and the junctions are perpendicular to the surface of the structure. A structure comprising said described PN junctions is called a vertical super-junction structure. In a conventional method for fabricating the super-junction structure, an epitaxial layer of a first conductivity type, e.g. N-type, is formed on a substrate of the first conductivity type. Then, a plurality of trenches is etched into the first conductivity type epitaxial layer using a first mask. A second conductivity type epitaxial layer, e.g. P-type epitaxial layer, is used to fill the trenches, and the surface of the second conductivity type epitaxial layer is leveled with the surface of the first conductivity type epitaxial layer. Hence, the trenches are filled with the second conductivity type epitaxial layer and are surrounded by the first conductivity type epitaxial layer. As a result, a super-junction structure with a plurality of vertical PN junctions is formed.
The above-mentioned method, however, still has many drawbacks. For instance, when comparing to conventional IGBT power devices, a power device with vertical PN junctions has a relatively high on-state resistance for the same voltage sustaining ability. A conventional way to reduce the resistance in the power device with vertical PN junctions is to fabricate trenches with a relatively high aspect-ratio. However, the fabrication of trenches with higher aspect-ratio is limited by technical means and high fabricating costs. In light of the above, there is still a need for fabricating a power device that would be capable of overcoming the shortcomings and deficiencies of the prior art.